I would guess a significant portion of people using the style (if not most), did so inspired by Windows, though

It was common across all not UNIX operating systems.

You will find it on MS-DOS, Amiga, OS/2, Mac OS.

It was based on what was common in ALGOL derived languages.

On UNIX you will find it on X Windows, and Motif.

Macintosh toolbox was Pascal first right? Or at least there was an era where it was. And I think this naming convention is kinda a pascal thing.

Yes, Apple is the actual creator of Object Pascal variant, and there was a Pascal based OS using P-Code for Apple II GS.